U.S. patent application number 10/580203 was filed with the patent office on 2007-03-29 for method and device for increasing the capacity of non-spread transmission systems.
Invention is credited to Marc Chenu-Tournier.
Application Number | 20070071135 10/580203 |
Document ID | / |
Family ID | 34566240 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070071135 |
Kind Code |
A1 |
Chenu-Tournier; Marc |
March 29, 2007 |
Method and device for increasing the capacity of non-spread
transmission systems
Abstract
A method for increasing the capacity of signal transmission
systems comprising N.sub.T users, a single-piece receiver receiving
the mixture of signals originating from the N.sub.T users including
at least the following steps: determining a qualitative information
Info(Qs) of the symbols estimated for each of the N.sub.T users,
transmitting this information Info(Qs) to a processing block
receiving an a priori information and designed to generate a
quality information Info(Qbs) on the bits forming the symbols,
transmitting the Info(Qbs) to a decoding step to obtain a
qualitative information on the encoded bits and Info(Qbu) on the
useful bits.
Inventors: |
Chenu-Tournier; Marc;
(Paris, FR) |
Correspondence
Address: |
LOWE HAUPTMAN GILMAN & BERNER, LLP
1700 DIAGNOSTIC ROAD, SUITE 300
ALEXANDRIA
VA
22314
US
|
Family ID: |
34566240 |
Appl. No.: |
10/580203 |
Filed: |
November 2, 2004 |
PCT Filed: |
November 2, 2004 |
PCT NO: |
PCT/EP04/53140 |
371 Date: |
May 23, 2006 |
Current U.S.
Class: |
375/324 |
Current CPC
Class: |
H04L 1/005 20130101;
H04L 1/0055 20130101; H04L 27/2647 20130101 |
Class at
Publication: |
375/324 |
International
Class: |
H04L 27/00 20060101
H04L027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2003 |
FR |
0314014 |
Claims
1. A method for increasing the capacity of signal transmission
systems comprising N.sub.T users, a single-piece receiver receiving
the mixture of signals originating from the N.sub.T users,
comprising the following steps: a) determining a qualitative
information of the symbols estimated for each of the N.sub.T users,
b) transmitting this information to a processing block receiving an
a priori information and designed to generate a quality
information, on the bits forming the symbols, and c) transmitting
the to a decoding step to obtain a qualitative information on the
encoded bits and on the useful bits.
2. The method as claimed in claim 1, wherein step a) is performed
using an MAP (Maximum a Posteriori) detector.
3. The method as claimed in claim 1, wherein the steps a) to c) are
repeated until the qualitative information is fairly constant.
4. The use of the method as claimed in claim 1, for transmitters
using one of the following modulation schemes: BPSK, QPSK,
OFDM.
5. The use of the method as claimed in claim 2, for transmitters
using one of the following modulation schemes: BPSK, QPSK,
OFDM.
6. The use of the method as claimed in claim 3, for transmitters
using one of the following modulation schemes: BPSK, QPSK, OFDM.
Description
[0001] The invention relates in particular to a method for
increasing the capacity of transmission systems by multiplying the
number of simultaneous senders in one and the same frequency band
and enabling the users to be separated in particular through the
use of iterative steps.
[0002] Known from the prior art are methods enabling simultaneous
transmission from different users. These normally rely on the use
of spreading codes, such as CDMA (Code Division Multiple Access),
MCCDMA (Multicarrier Code-Division-Multiple-Access) and/or on the
use of multiple-antenna receivers.
[0003] The method according to the invention relies in particular
on a novel approach which exploits the independence of the binary
streams (signals originating from the different senders), channel
encoding and the difference of the majority of the propagation
channels.
[0004] The invention relates to a method for increasing the
capacity of signal transmission systems comprising N.sub.T users, a
single-piece receiver receiving the mixture of signals originating
from the N.sub.T users. It is characterized in that it includes at
least the following steps: [0005] a) determining a qualitative
information Info(Qs) of the symbols estimated for each of the
N.sub.T users, [0006] b) transmitting this information Info(Qs) to
a processing block receiving an a priori information and designed
to generate a quality information, Info(Qbs), on the bits forming
the symbols, [0007] c) transmitting the Info(Qbs) to a decoding
step to obtain a qualitative information Info(Qbs) on the encoded
bits and Info(Qbu) on the useful bits.
[0008] The method according to the invention allows, notably to:
[0009] increase the bit rate of the transmission systems that use
existing standards for the user stations by modifying only the
access point, [0010] simply separate the different binary streams
by exchanging information between the demodulation block and the
decoding block, [0011] increase the capacity of the transmission
systems by multiplying the number of senders without using
multiple-antenna receivers and without using spectrum spreading
techniques, in the context of normal operation.
[0012] Other advantages and characteristics of the invention will
become more apparent from reading the description that follows of a
detailed example, given purely for illustration and by no means
limiting, with appended figures in which:
[0013] FIG. 1 shows a global diagram of the method according to the
invention, and
[0014] FIG. 2 shows a detailed generic diagram of the steps of the
method according to the invention.
[0015] FIG. 1 diagrammatically represents the various steps of the
method according to the invention used in a communication or
transmission system comprising a number of users or senders
N.sub.T, and a receiver comprising, for example, a monosensor R.
The various senders transmit the symbols simultaneously in the same
frequency band, for example. Since the communications are normally
disturbed by a propagation channel, a channel encoding is
conventionally used. The method uses, for example, this encoding to
perform the demodulation.
[0016] FIG. 2 shows the generic diagram of an exemplary monosensor
receiver.
[0017] It comprises a module 1 for receiving the mixture of the
signals sent by the N.sub.T users or senders, separating the
different users and supplying a qualitative information, Info(Qs),
of the symbols estimated for each of the users N.sub.T (for
example, a probability of having received such a symbol). The
module 1 can be a detector in the maximum a posteriori (MAP) sense
which provides a probability of the symbols sent for the different
senders N.sub.T relying on an a priori information. The information
on the estimated symbols Info(Qs) is then transmitted to a
processing block which will deduce from this a quality information
on the bits that form the symbols Info(Qbs). This information
Info(Qbs) is then transmitted to the decoding block 4i (a
de-interleaving procedure can be applied beforehand) which, in
turn, will produce a qualitative information Info(Qbs) on the
encoded bits and Info(Qbu) on the useful bits.
[0018] The information on the encoded bits Info(Qbs) can be reused
in order to re-estimate an information on the symbols as described
previously. The information on the useful bits is deduced from the
information on the encoded bits, for example, by the decoding
procedure.
[0019] A prior processing of the informations transmitted to the
different blocks may prove necessary for the method to operate
correctly. In the example described below, the information
previously used to estimate a new qualitative information on a bit,
is subtracted in order to supply only a real new information to the
block receiving it.
[0020] These steps are repeated, either a fixed number of times, or
until a criterion is satisfied (for example, the qualitative
informations cease to change).
[0021] The way the method operates is described below as an example
for the user N.sub.1.
[0022] The information on the probability of symbols sent
P(a.sup.1.sub.Nu|yi), Info(Qs), is transmitted to a device 2.sub.1
(or demapping) having the main function of providing an information
on the probability of the bits sent L.sub.D(c.sub.k.sup.1) by the
user N.sub.1, Info(Qbs). This information is, for example, sent in
a de-interleaver 3.sub.1, then to a BCJR type algorithm (encoding
block 4i) in order to obtain the probability of the encoded bits
L.sub.c(c.sub.k.sup.1) (qualitative information on the encoded
bits, Info(Qbs), and the useful bits, Info(Qbu)). This latter
information (L.sub.c(c.sub.k.sup.1)) is subtracted from the first
information L.sub.D(c.sub.k.sup.1) of probability on the bits
(quality information on the bits forming the symbols Info(Qs))
before going on to the de-interleaver. It is also sent to an
interleaver 5.sub.1, then to a device 6.sub.1 having a mapping
function, before being reinjected into the device 1 which uses this
information Info(Qs) in the step for obtaining the probability of
the symbols sent.
[0023] The mapping and demapping devices, the interleavers and the
de-interleavers are devices known to those skilled in the art which
are not detailed in the present description.
[0024] In order to illustrate the method according to the
invention, the example that follows is given in the case of
frequency-synchronized OFDM (orthogonal frequency division
multiplexing) senders. For this so-called multi-carrier or parallel
waveform, the different symbols are transmitted simultaneously on
orthogonal subcarriers.
[0025] In this exemplary embodiment, the different senders use a
convolutional code as in the Hiperlan/2 or IEEE802.11a
standard.
[0026] The receiver conventionally performs a discrete Fourier
transform (DFT) on a predetermined timeslot to estimate the
transmitted symbols.
[0027] In the case of multiple sendings that are
frequency-synchronized and sufficiently synchronized in time to
avoid the inter-symbol interference, the signal received by the
receiver after the Fourier transform is given by:
y=F.sub.2I.sub.{overscore (PC)}HI.sub.PCF.sub.1a+b (1) in which
[0028] y is the received signal represented by a vector
(N.sub.SP).times.1 with N.sub.SP being the number of subcarriers,
[0029] a is the dimension vector (N.sub.T.times.N.sub.SC).times.1
containing the symbols transmitted by the N.sub.T senders. The
N.sub.T first elements are the symbols transmitted on the first
subcarrier, [0030] F.sub.1={tilde over (F)}.sub.1I.sub.N.sub.T is
the matrix performing the DFT on sending with I.sub.N.sub.T being
the dimension identity matrix N.sub.T and the operator being the
Kronecker product, [0031] I.sub.PC= .sub.PCI.sub.N.sub.T is the
dimension matrix
N.sub.T(N.sub.N.sub.CP+N.sub.DFT).times.N.sub.TN.sub.N.sub.DFT
which performs the insertion of the cyclic prefix (specific to
OFDM), [0032] H is the matrix of the samples representing the
propagation channel, of dimension
(N.sub.T(N.sub.N.sub.CP+N.sub.DFT)+N.sub.H).times.N.sub.T(N.sub-
.N.sub.DFT+N.sub.CP) with N.sub.H being the maximum length of the
propagation channels, [0033] I.sub.{overscore (CP)}=
.sub.{overscore (CP)}I.sub.N.sub.T is the matrix that performs the
synchronization and removes the cyclic prefix, [0034] F.sub.2 is
the matrix that performs the DFT on the receiver, [0035] b is the
dimension vector N.sub.SP.times.1 containing the samples of the
noise considered in this example as temporally white noise.
[0036] The matrix K defined below is a rotating block matrix and as
such can be expressed as: K=F.sub.2.sup.HGF.sub.1 (2) in which G is
a diagonal block matrix and F.sub.1 and F.sub.2 are DFT
matrices.
[0037] Since I.sub.{overscore (PC)}HI.sub.PC is a circulating
block, the received signal can be expressed as: y=Ga+b (3) in which
G is a diagonal block matrix with blocks of size
1.times.N.sub.T.
[0038] Therefore, for the subcarrier i, the vectorial observation
y.sub.i can be expressed as: y.sub.i=G.sub.ia.sub.i+b.sub.i (4) in
which G.sub.i contains the elements of the frequency response of
the channel.
[0039] In this case, since we are using only one receiver, G is a
vector of size 1.times.N.sub.T.
[0040] Thus the observation y.sub.i is scalar and is expressed: y i
= i = 1 N T .times. .times. h i .times. a i + b i ( 5 )
##EQU1##
[0041] In this case, the detector in the MAP sense supplies the
following probabilities: (qualitative information of the estimated
symbols--probability of the symbols sent for the different senders)
p .function. ( a i k = a .times. | .times. y i , G i , .sigma. 2 )
= a t .di-elect cons. A a k .times. .times. p .function. ( y i
.times. | .times. a t , G i , .sigma. 2 ) .times. p .function. ( a
t ) a t .di-elect cons. A .times. .times. p .function. ( y i
.times. | .times. a t , G i , .sigma. 2 ) .times. p .function. ( a
t ) ( 6 ) ##EQU2## in which .sigma..sup.2 is the variance of the
noise and A.sub.a.sup.k is defined by: A.sub.a.sup.k={a|a.sup.k=a}
(7)
[0042] A.sub.a.sup.k contains the symbol vectors a which have the
symbol a in the position k.
[0043] These probabilities are then used to calculate the
probability of the bits forming the symbols: L .function. ( c ) =
log .times. a .di-elect cons. A + .times. .times. p .function. ( a
.times. | .times. y i , G i , .sigma. 2 ) a .di-elect cons. A -
.times. .times. p .function. ( a .times. | .times. y i , G i ,
.sigma. 2 ) ( 8 ) ##EQU3## in which A.sup.+ is the set of symbols
in which the bit c is 1 and A.sup.-is the set of symbols in which
the bit c is 0. These quantities are then used to calculate:
L.sub.D(C)=L(C)-L.sub.c(c) (9) which is supplied to the decoding
block. In the figure, the equation (9) is represented by the
indices L.sub.D(c.sub.k.sup.i)=L(c)-L.sub.c(c.sub.k.sup.i).
[0044] The term L.sub.c(C) (L.sub.c(c.sub.k.sup.i) in FIG. 2)
corresponds to the a priori information derived from the preceding
decoding. On the first iteration, L.sub.c(c)=0. These values
L.sub.D(c) (L.sub.D(c.sub.k.sup.i) in FIG. 2) are the inputs of the
flexible decoder which, in the example, is a BCJR type algorithm,
described, for example, in the document by L. Bahl, J. Cocke, F.
Jelinek, and J. Raviv, entitled "Optimal decoding of linear codes
for minimizing symbol error rate", IEEE Trans. Inform. Theory, pp.
284-287, March 1974. This block is not described any more in
detail.
[0045] This decoder supplies both the probability of the useful
bits (before encoding) and the probability of the encoded bits that
form the symbols.
[0046] The method is used, for example, for BPSK (Bit Phase Shift
Keying) or QPSK (Quadrature Phase Shift Keying) modulation
schemes.
* * * * *